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CONSTRUCTING A SWAT MODEL OF THE SUNRISE RIVER WATERSHED, EASTERN MINNESOTA
James E. Almendinger, St. Croix Watershed Research Station, Science Museum of Minnesota
The Sunrise River watershed in eastern Minnesota comprises valued water resources with multiple impairments due at least partially to nonpoint-source pollution. Computer modeling of watershed processes is an important tool to help show where such pollution may originate and which mitigation strategies may be most effective. The Soil and Water Assessment Tool (SWAT) is a modeling program designed to predict the long-term effect of land management on nonpoint-source pollution in large watersheds. A SWAT model was constructed from available topographic, hydrographic, soils, land cover, crop cover, livestock, and climate data sets. The model was calibrated to crop yields, stream flow, sediment load, and phosphorus load in the watershed, based on monitoring data from six sites. The monitoring data indicated that the upper subwatershed, probably because numerous lakes and wetlands, was a fairly minor contributor of nonpoint-source sediment and phosphorus. The North Branch subwatershed contributed about 27% of the sediment and 33% of the phosphorus reaching the watershed outlet. However, the lower subwatershed, from below the outlet to Carlos Avery Wildlife Management Area to the village of Sunrise, contributed the most sediment (69%) and nonpoint-source phosphorus (44%) of any such subwatershed. Much of the sediment appeared to be derived from channel erosion or other such riparian source, based on modeled amounts of field erosion. Calculated yields of sediment and phosphorus for the Sunrise watershed were in the same range as for other tributaries in the lower St. Croix basin.
Data critical for model calibration were supplied by the Minnesota Pollution Control Agency, Chisago County Soil and Water Conservation District, U.S. Army Corps of Engineers, U.S. Geological Survey, and Minnesota Department of Natural Resources.